Reverberant vs Direct field strengths

[Zilch]

Toole and Olive hate the room, and the speakers they appear to lionize are mainly configured to be smooth and flat over a rather narrow frontal angle, in spite of those men paying lip service to smooth (but subdued) response at wider off-axis angles. I would not have minded it so much if Toole had come down against ultra-wide dispersion in his book, and pointed out what he considered to be the problems with that approach. However, he made no mention of it at all, except as the design might be beneficial to surround speakers.

Toole goes to considerable length in his book to outline why ultra-wide dispersion is largely irrelevant to its primary focus, which is multi-channel HT.

While the Toole/Olive metric incorporates omnidirectional power response, they have long since moved on from outmoded '70s perspectives regarding loudspeaker design and room interaction.

[Zilch]

One important aspect of multi-channel home theater (not to mention multi-channel music playback) is to have as diffuse a soundfield as possible, in order to better simulate spaces larger than typical home-listening areas - even rather big ones like mine.

Please, Howard, post more high-resolution pics of your rather big listening space augmented with multi-channel processing to overcome the deficiencies of ultra-wide dispersion Allisons in simulating a realistic performance presentation....

[speaker dave]

Reverberant field simulations.

This is somewhat relevant to our Geddes discussion but more directly relevant to this older thread so I've attached it here.

I'm doing some work on simulating a loudspeaker in a reverberant field. As has been discussed on a number of threads the measurement of a speaker in a live room is a combination of its direct response, its total radiated power, the varying absorption of the room and the distance from source to listener. I need this for work and also because I'm thinking of writing and AES paper on the history and falacy of X curve cinema equalization.

The simulation is an excel spread sheet for room acoustics that adds up all the surfaces of the room with defined abosrption for each surface. This gives reverb. time and room constant vs. frequency. I've added a source with flat direct field or anechoic response and a 1/3rd octave defined directivity index. I then calculate the response at various distances as you move away from the speaker, culminating with the response at a distance in a purely reverberant field. This is always a combination of the direct sound, falling off with distance, and the reverberant field that is (fairly) constant around the room.

The hypothetical speaker has rising directivity and a power response hole at crossover. Although its response is flat on axis (defined as 100dB for all frequencies at 1m) as you move away the high frequency "deadness" of the room and the radiated power of the speaker start to impact the measured response.

Of course we can still debate whether the reverberant field curves are what we hear.

David

[Zilch]

YES!

The great marshmallow experiment LIVES!

[Well, in SIM, at least.... ]

[genek]

I can see how the marshmallow test could enable one to take some measurements of a reverberant field. but how that test or any other that mixes reverberant and direct could ever settle the question of whether one or the other dominates the listening experience escapes me. I think you'd have to set up a test in which direct is somehow eliminated and compare the subjective experience to that of the everyday mix. Perhaps some sort of "anti-anechoic chamber," in which the walls, floor and ceiling are arrayed with speakers that output Dave's reverberant field curve...

[speaker dave]

I can see how the marshmallow test could enable one to take some measurements of a reverberant field. but how that test or any other that mixes reverberant and direct could ever settle the question of whether one or the other dominates the listening experience escapes me. I think you'd have to set up a test in which direct is somehow eliminated and compare the subjective experience to that of the everyday mix. Perhaps some sort of "anti-anechoic chamber," in which the walls, floor and ceiling are arrayed with speakers that output Dave's reverberant field curve...

I think that (what dominates perception) is the essence of the long debate represented by this thread. One side thought that the in-room curve, primarily tied to the speake'rs power response, defined the perceived balance of the speaker. The other side (me) thought that the ear could hear through to the direct sound field and generally ignore the later arriving reverberent field.

I agree that a test that let you manipulate the direct or reverberent field is the answer. I've referred a couple of times to a paper that Lipshitz and Vanderkooy did, where they placed a Quad ESL 63 sideways on top of a KEF 104.2. With the ESL 63 sideways firing the listener would be on its null and would not hear it directly. That allowed them to independently manipulate the direct and reverberent field and come to some conclusions.

David

[genek]

The other side (me) thought that the ear could hear through to the direct sound field and generally ignore the later arriving reverberent field.

Couldn't this be demonstrated by putting the speakers in an anechoic chamber? If they sound the same to listeners there as they do in a normal room, then the reverberant field in the normal room is contributing nothing significant, yes?

[Zilch]

The essence of the marshmallow test is suggested by Toole: measure the draw-away curves and plot how the SPL drops with distance.

A diffuse, steady state reverberant field as predicted by the Beranek model would level it off at greater distances. Toole demonstrates that it doesn't happen in small rooms.

The marshmallows are a patent Zilchster ploy to divert the experimenter's attention from the data 'til the deed is done and the results posted.

Keeping the dog from eating the marshmallows is an essential element in this. The experimenter not eating the marshmallows serves to certify their dedication to science in pursuit of truth.

[Howard's reviews did publish in the Jan and Feb issues of AudioXpress, BTW.... ]

[genek]

If, as Dave says, theories in this matter are based on the idea that listeners are ignoring one type of sound in favor of the other, then no test that produces numerical data only will ever settle arguments based on subjective perceptions. Human beings are capable of ignoring really obvious stuff if they're determined to do so. Someone is going to have to build a test chamber that can be switched between direct-only, reverberant-only and a direct-reverberant mix, put a bunch of people inside it and do double-blind A/B/A+B testing.

[Zilch]

Someone is going to have to build a test chamber that can be switched between direct-only, reverberant-only and a direct-reverberant mix, put a bunch of people inside it and do double-blind A/B/A+B testing.

Not my gig.

But, help me now, if it's not there in the first place, then there's nothing to evaluate.

General consensus seems to be anything delayed longer than ~10 - 20 ms may contribute to perceptions of spaciousness, but it's dialed out psychoacoustically with respect to spectral balance, and the direct field dominates, even if there is a reverberant one. It's the distinction between early and late reflections, and small vs. larger rooms, according to Geddes.

[genek]

Not my gig.

But, help me now, if it's not there in the first place, then there's nothing to evaluate.

General consensus seems to be anything delayed longer than ~10 - 20 ms may contribute to perceptions of spaciousness, but it's dialed out psychoacoustically with respect to spectral balance, and the direct field dominates, even if there is a reverberant one. It's the distinction between early and late reflections, and small vs. larger rooms, according to Geddes.

Not mine either.

There's a long history of people in audio arguing that measurements (or the lack thereof) don't prove that something they believe exists does not. Nothing here holds any promise of changing that.

And the never-ending chain of disagreement in this forum amply demonstrates that "according to" carries no weight in the debate, whether the name invoked is Geddes, Villchur or Allison.

Like Carl in the other thread, I'm still waiting for somebody to offer something that isn't a reshash or what's already been posted many times over.

[Zilch]

+6 dB certainly counts for something; all we need is the AR3a DI, now....

[genek]

+6 dB certainly counts for something; all we need is the AR3a DI, now....

Do you still have the pair you were measuring last year...?

[Zilch]

Do you still have the pair you were measuring last year...?

Did that, and confirmed Allison's findings of 40 years ago, so we'll just use his data to compute the DI, and when the dispute revs into high gear, nobody'll be impugning my competence.

I've moved on to modding the AR3a, but needless to say, the exigencies of staying ahead of higher priorities have limited my availability for pursuit of that most worthy endeavor.

[i wonder if Howard took notice of the Steampunk EconoWave in the January AudioXpress.... ]

[speaker dave]

Someone is going to have to build a test chamber that can be switched between direct-only, reverberant-only and a direct-reverberant mix, put a bunch of people inside it and do double-blind A/B/A+B testing.

A number of people have done that. Soren Bech did it an found that in a simulated room the three boundaries of the corner generally defined the perceived bass response. The only other significant reflection was the floor in front of the speaker that added midrange colorations. Above that range the direct response was the primary definer of perceived frequency response. Reflections later in time didn't impact frequency response.

Lipshitz and Vanderkooy did the experiment with the ESL 63 adjusting the power response and found that flat sound power at the expense of messed up direct response was always wrong. Flat power with flat on axis response was "too bright" and holes in the power response were pretty benign.

Kates (KK knows him) did an excellent paper wher he modeled the hearing system and came up with a measuring scheme that was subjectively correct. It used critical band filtering and time windowing, which again focused on the direct response at high frequencies and progressively longer windows for lower frequencies. Salmi did a similar measuring scheme.

There may not be much agreement on this forum but researchers of the last 20 years seem to have come to a pretty clear consensus.

David

[genek]

A number of people have done that.

This thread might have been 140 posts shorter if people had described real-world test results instead of just hurling dueling theorists at each other...

[genek]

And if you listen to your favorite directional speakers in your favorite listening room and then haul them outdoors (on a nice day, hopefully) and listen to them again out there you will find that even the most directional speakers will sound different from how they sounded indoors.

If the debate was whether reverberant exists or contributes, I would think this exercise might settle it, but it obviously hasn't been universally convincing about "dominates."

[speaker dave]

If this is the case then the successful LVR sessions Villchur did with the AR-3 make no sense at all. The AR-3 had anything but a flat direct-field response (Allison and Berkovitz showed pretty much the same thing with the AR-3a, and went on to demonstrate how smooth the power response was), and so the speaker should have flunked those demonstrations big time. The demonstrations actually should not have fooled anybody even slightly. What's more, the sales success of various AR models over the decades (AR-3, AR-3a, AR-LST, etc.) shows that if what the research noted above is true a whole generation of acoustic-instrument-loving audio enthusiasts were hearing deficient.

On the other hand, if the LVR demos were as convincing as many people say (including Julian Hirsch, who was wowed by the results), then the whole direct-field premise outlined above is bunk.

Howard Ferstler

I have no interest in re-argueing the whole debate yet again, but let me just point out a few flaws in your logic.

Even Vilchur admitted that the AR3 needed some EQ to sound most convincing in the LvR tests.

The success of the demonstrations proves that they were well conducted. It does not prove that the AR3 was the best speaker of the time or the best ever since, merely that it was up to the task (as the Edison Victrola had been years before).

Sales of products aren't a strong proof of performance. Many great product fail and many mediocre products succeed. I'm sure you can think of your own examples here.

All you can claim for the AR3 and AR3a was that they had fairly flat response when their individual drivers were measured in ideal 2pi conditions. This is not proof that they wouldn't have been even better sounding as systems had they reduced the baffle effects, cleaned up the edge reflections, or achieved better free field blending of the drivers via more sophisticated crossovers. This was all done in later AR products, where they inferior because of it?

I note that you mention smooth power response rather than flat power response, which is closer to the crux of the previous debate. Smooth power response is relatively easy to achieve as it reduces loudspeaker design from a 3 dimensional issue to a 1 dimensional one.

Sorry I re-opened the thread. I was just pleased that my simulations were starting to work.

David

[speaker dave]

This thread might have been 140 posts shorter if people had described real-world test results instead of just hurling dueling theorists at each other...

The Lipshitz and Vanderkooy paper is as real world as you can get. If you have any theorists or papers at odds with the ones I mentioned I would like to hear of them and I promise to read them.

I can't imagine anyone has read the papers I keep mentioning.

David

[genek]

The Lipshitz and Vanderkooy paper is as real world as you can get. If you have any theorists or papers at odds with the ones I mentioned I would like to hear of them and I promise to read them.

I can't imagine anyone has read the papers I keep mentioning.

I wasn't questioning the reference, just referring to it being mentioned in post #145 instead of, say, #4 or #5.

As far as reading the papers, (1) I probably wouldn't be able to make any sense of them if I did, and (2) while I can't speak for anyone else here, your summary is good enough for me. I wish everyone who had one of these references to toss into the mix would summarize them this way.

[speaker dave]

I wasn't questioning the reference, just referring to it being mentioned in post #145 instead of, say, #4 or #5.

Sorry Gene, I was letting my frustration get the better of me.

David

[Zilch]

Alison and Berkovitz disproved this decades ago.

Allison and Berkovitz disproved their own theories, as I have profusely demonstrated in these pages, and you refuse to appreciate that fact because it goes to the very core of your outmoded belief system as to how loudspeakers and rooms work.

If this is the case then the successful LVR sessions Villchur did with the AR-3 make no sense at all.

Drivel. They were contrived promotional hype, not science, and the last best evidence of the inanity of your argument, fully deserving of the short shrift accorded them by Toole, which is where all of this began.

I can better Villchur and Allison in accomplishing their wide dispersion objectives using constant directivity in a mere 30 seconds, as I have suggested several times before here.

Actually, I was hoping that Carl would pick up on it, and build something to measure. Neither was I successful in tempting you to step out to your workshop and dirty it up with sawdust. Bah!

This thread might have been 140 posts shorter if people had described real-world test results instead of just hurling dueling theorists at each other...

Wishful thinking. That ain't what the blather is about....

[genek]

Sixth, I am not sorry you re-opened this thread at all. It introduces the issue to newcomers who may have joined up since the last series of observations.

You really think anybody's still reading this topic besides the four principal posters? The only reason I'm still here is to see which of you is going to make the post that shuts it down.

[genek]

Well, there is always the chance that by staying here you will learn something.

That was actually happening for the first 20-30 posts in the thread. Then it went into reruns.

[Zilch]

I suggest you get busy and write....

zzzzzzz